Chemical polishing of metallic sodium

ABSTRACT

A method of preparing metallic sodium specimens for optical metallographic studies to ascertain the purity thereof whereby the sodium is polished in a bath of containing an aliphatic ketone and an aliphatic alcohol.

United States Patent [72] Inventors Hugh Solomun Isaacs Shoreham;

Robert M. Singer, East Islip, both of NY.

[21] Appl. No. 49,188

[22] Filed June 23, 1970 [45] Patented Nov. 16, 1971 [73] Assignee The United States of America as represented by the United States Atomic Energy Commission [54] CHEMICAL POLISHING 0F METALLIC SODIUM 3 Claims, No Drawings [52] us. CI 156/20,

[5i] lnt.Cl C23; 5/02 [50] Field ofSearch l56/2, I8, 20; 252/79.l

[56] References Cited UNITED STATES PATENTS 3,072,515 1/1963 Smolinski l56/20 Primary Examiner-William A. Powell Attorney-Roland A. Anderson ABSTRACT: A method of preparing metallic sodium specimens for optical metallographic studies to ascertain the purity thereof whereby the sodium is polished in a bath of containing an aliphatic ketone and an aliphatic alcohol.

CHEMICAL POLISHING F METALLIC SODIUM PRIOR ART The corrosion of containment materials by liquid sodium in fast breeder reactors is influenced by particulate impurities in the sodium. Optical metallographic studies are an excellent method of studying sodium for particles. However, the extreme softness and high chemical activity of sodium have complicated its mechanical preparation for optical metallographic studies.

SUMMARY OF THE INVENTION We have discovered a method of preparing metallic sodium for metallographic examination by optical microscopy comprising securing a freshly cut solid specimen of metallic sodium substantially free of oxide layer and mineral oil; immersing the specimen in a bath composed of from about 2 to about 90 volume percent of an aliphatic ketone having a melting point below 50 C. (e.g. acetone, methyl ethyl ketone), and from about to about 98 volume percent of an aliphatic alcohol having a melting point of below 50 C. based on the total volume of the bath for a period of time sufiicient to form a specular surface on the face of the specimen; the presence of the alcohol prevents clouding of the bath by having the reaction products go into solution and slows down the rate of reaction while the specimen is in the bath. Sodium specimens when immersed in the baths of our invention for periods of time ranging from 1 to 60 seconds develop splendent surfaces which render them easily examinable by optical means. After the specimen has been removed from the bath, it is washed with a solvent which is inert to sodium to remove any traces of the bath (e.g. petroleum ether, aliphatic paraffins, etc.).

Acetone and methanol are the preferred ingredients for the bath as they give the best overall results for the preparation of sodium for metallography. When analytical reagent grade acetone, methanol and petroleum ether are used, no precautions need be taken to prevent oxygen or water vapor dissolving in any of the organic liquids used. U.S.P. grade mineral oil is used to protect the sodium during examination. The reaction of sodium with acetone alone rapidly heated the sodium. The temperature of the sodium when polished in pure acetone was measured with a thermocouple imbedded in the sodium and was found to rise within two seconds to 70 C. The addition of methanol has a marked effect on reducing the reaction rate of the pure acetone and mixtures of acetone and methanol are used when large sodium samples, having a surface area greater than about 6 cm.', were polished. Mixtures of 5 to 50 percent methanol in acetone gave polished surfaces but the luster decreased with increased amounts of alcohol.

When sodium is polished for metallography the following procedure can be adopted. The sodium is held metal tweezers and always agitated, as this assists in both the washing of the sodium and in obtaining a smoother surface.

Sodium samples about 5Xl0 mm. and over 2 mm. thick are cut and prepared under mineral oil. The mineral oil is removed by washing in petroleum ether. If the sample has a thick layer of oxide prior to polishing, the layer is removed by reacting with pure methanol for periods of 2 to 3 seconds. The sample is then placed in a mixture of acetone vol. percent) and the methanol (20 vol. percent) and agitated. The time required for polishing is usually less than 10 seconds. The sample is then dipped into pure acetone for 2 seconds and immediately afterwards it is washed in petroleum ether. Tamishing of the sodium results if the petroleum ether is contaminated with the polishing solution from repeated use or if the sample itself carries out excess polishing solution in cracks, holes or thick surface oxide layers. The presence of alcohol in the petroleum ether increase the probability of tarnishing. The sodium is then placed in mineral oil and finally in a flat-bottomed glass container filled with mineral oil and viewed from the bottom. It can remain for several hours if US.

grade mineral oil is used to shield it from the atmosphere After preparation the samples remalned unox|d|zed w|thout damage for over an hour when no precautions were taken to remove oxygen or water from the oil. The samples were in excellent condition for optical metallographic examination.

We claim:

1. A method of preparing metallic sodium for metallographic examination by optical microscopy comprising securing a freshly cut solid specimen of metallic sodium substantially free of oxide layer, immersing the specimen in a liquid bath composed of from 2 to about volume percent of an aliphatic ketone having a melting point below 50 C. and from about l0 to about 98 volume percent of an aliphatic alcohol having a melting point below 50 C. until said specimen develops a splendent surface, removing said specimen from the bath and washing said specimen with a solvent which is inert to sodium to remove any remains of the bath from the surface of the specimen.

2. A method in accordance with claim 1 wherein in the aliphatic ketone employed is acetone.

3. A method in accordance with claim 2 wherein the aliphatic alcohol employed is methyl alcohol.

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2. A method in accordance with claim 1 wherein in the aliphatic ketone employed is acetone.
 3. A method in accordance with claim 2 wherein the aliphatic alcohol employed is methyl alcohol. 